Exposure Controls

 

No digital camera can capture every tone available in a scene. In other words you can’t record what you see with your eyes. Some detail in dark areas is lost because not enough photons are captured by the sensor, and details in light areas vanish when pixels in a sensor are flooded with more light than they can handle.

The range from the darkest detailed picture elements to the brightest is called the dynamic range, and the goal of proper exposure is to make sure that the most important tones in an image fall into that range.

Getting a good exposure is relatively easy, but getting the best exposure can be tricky.

 

Film Speed - ISO

 

     ISO determines how sensitive the image sensor is to light. The more sensitive the sensor is, the better it can capture images in low light levels. Wikipedia has a very technical explanation about what film speed is, but honestly I don’t think you will ever need that much info (but if you’re curious, you can read about it here.

 

All you need to know is that ISO determines the sensitivity of your sensor.

 

If a combination of shutter speed and aperture don't deliver enough light, you can boost your ISO. The penalty is red and green spots (noise) over your image.

 

Depth of Field

     

     Depth of field (DOF) is the distance between the nearest and farthest objects in a scene that appear acceptably sharp in an image. Although a lens can precisely focus at only one distance at a time, the decrease in sharpness is gradual on each side of the focused distance, so that within the DOF, the unsharpness is imperceptible under normal viewing conditions.

 

The factors which affect depth of field are: aperture, focal length and distance to subject.

 

A short depth of field can be very useful when you want to isolate your subject from the background (portraits, macro), while a large depth of field is great when you want every detail to be in focus (landscape photography).

 

Aperture

     Your DSLR camera sensor needs light to create an image. There are two ways it can get the light that it needs: keeping the shutter open for a long period of time or by opening the aperture as wide as possible. 

The lens aperture is an adjustable control that determines the width of the opening that admits light to the sensor. The wider the aperture, the more light that can reach the sensor, making it possible to take pictures in dimmer light. The easiest way to imagine this is to think of an aperture as the pupil of your eye. When it’s bright outside, your pupils contract, letting in less light. When it’s dim, your pupils dilate. A narrow aperture reduces the amount of light that reaches the sensor, letting you avoid overloading the imaging device in very bright light. Aperture is used in tandem with shutter speed to control the exposure; and is measured in f-stops.